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Distribution of b-value in the Middle America Trench, near Nicoya Peninsula, Costa Rica

Distribution of b-value in the Middle America Trench, near Nicoya Peninsula, Costa Rica. Abhijit Ghosh A. V. Newman, A. M. Thomas, G. T. Farmer School of Earth & Atmospheric Sciences Georgia Tech. Outline of the talk. Basics of plate tectonics Why this study is important What is b-value…

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Distribution of b-value in the Middle America Trench, near Nicoya Peninsula, Costa Rica

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  1. Distribution of b-value in the Middle America Trench, near Nicoya Peninsula, Costa Rica Abhijit Ghosh A. V. Newman, A. M. Thomas, G. T. Farmer School of Earth & Atmospheric Sciences Georgia Tech A. Ghosh, EAS, Georgia Tech

  2. Outline of the talk • Basics of plate tectonics • Why this study is important • What is b-value… • Data processing and results • Discussions • Summary A. Ghosh, EAS, Georgia Tech

  3. Plate tectonic map http://earthquake.usgs.gov/ A. Ghosh, EAS, Georgia Tech

  4. Plate boundaries http://www.permatopia.com/wetlands/images/ A. Ghosh, EAS, Georgia Tech

  5. Why this study is important Lowman and Montgomery, 1998 A. Ghosh, EAS, Georgia Tech

  6. Study area: Middle America Trench A. Ghosh, EAS, Georgia Tech

  7. Seismic network and earthquake location 1-D global velocity model 3-D local velocity model A. Ghosh, EAS, Georgia Tech

  8. What is ‘b-value’… : frequency-magnitude distribution log10N = a – b. M M = Magnitude of earthquakes N = number of earthquakes equal or greater than M b = slope of the line a = intercept of the line (seismicity rate) A. Ghosh, EAS, Georgia Tech

  9. b-value in the study area b = 1.29±0.03 a = 6.19±0.1 A. Ghosh, EAS, Georgia Tech

  10. Spatial variation of Mc A. Ghosh, EAS, Georgia Tech

  11. Spatial variation of b-value A. Ghosh, EAS, Georgia Tech

  12. b-value error A. Ghosh, EAS, Georgia Tech

  13. Interpretation Norabuena et al., 2004 A. Ghosh, EAS, Georgia Tech

  14. Summary • b-value varies spatially in the Middle America Trench (MAT), near Nicoya Peninsula • Anomalously low b-value zone detected • May indicate locked part of MAT • Supported by independent geodetic model • b-value mapping may be used to identify locked portion of subduction zone A. Ghosh, EAS, Georgia Tech

  15. Thanks and Questions ?? A. Ghosh, EAS, Georgia Tech

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